prior art exhaust muffler has been formed from a plurality of tubes disposed in a generally parallel array and supported by a plurality of transverse baffles. An outer shell defined by a generally tubular sheet of metal is disposed around the array of tubes and generally in contact with the transverse baffles. The outer shell typically has been of constant elliptical or circular cross section along its entire length. An outer wrapper then is disposed about the tubular shell to dampen shell noise. A pair of opposed end caps are secured to the opposed ends of the tubular shell and outer wrapper and are provided with at least one aperture extending therethrough. The spaces within the wrapped outer shell and intermediate adjacent baffles or intermediate a baffle and an adjacent end cap define chambers within the muffler. Nipples extend through the apertures in the end caps to communicate with the tubes and/or chambers within the prior art muffler. Selected tubes are provided with perforations or louvers to permit communication with the chamber through which the tubes pass. These chambers are generally defined as expansion chambers, and permit exhaust gases traveling through the tubes to expand into the chamber. Expansion chambers contribute substantially to the noise attenuation functions of the prior art muffler. Frequently, however, low frequency noises may not be adequately attenuated by the expansion chambers. Thus, the prior art muffler typically has included at least one low frequency resonating chamber into which a tuning tube extends. The volume of the low frequency resonating chamber and the length and cross section of the tuning tube have been selected in accordance with the specific frequency of the low frequency noise to be attenuated.
The above described prior art wrapped outer shell mufflers have performed well. However, these prior art wrapped outer shell mufflers have required a large number of separate components that must be accurately assembled in labor intensive manufacturing processes. Furthermore, the elongated generally cylindrical configurations of these prior art muffler have made it difficult to fit the prior art wrapped outer shell muffler within the limited available space on the vehicle.
The prior art also includes mufflers formed at least in part by stamp formed components. The typical prior art muffler formed entirely form stamp formed components has consisted of a simple array of perforated tubes disposed within an expansion chamber. Although stamp formed mufflers of this simple construction have attenuated some of the noises associated with exhaust gases, they generally have failed to attenuate at least one range of low frequency noises.
Certain prior art mufflers formed at least in part from stamp formed components have attempted to deal with low frequency noise attenuation. In particular, U.S. Pat. No. 3,140,755 which issued to Tranel on July 14, 1964, shows a muffler formed to include a main tube and a plurality of dead end spur tubes intersecting the main tube. The spur tubes are of different lengths with the number and configuration of spur tubes being selected to attenuate specific low frequency noise. The muffler shown in U.S. Pat. No. 3,140,755 does not provide the combination of an expansion chamber and plural low frequency resonating chambers communicating with an array of tubes, and therefore would be of limited effectiveness in attenuating sounds associated with a vehicular engine.
Japanese Patent No. 59-43456 shows a muffler formed at least partly from stamp formed components and including one low frequency resonating chamber and an expansion chamber. However, to achieve the low frequency resonating chamber, the muffler shown in Japanese Pat. No. 59-43456 must include a plurality of separate tubular members to extend through the outer shell of the muffler, pass entirely through the low frequency resonating chamber and be secured to stamp formed components well within the muffler. Thus, the muffler shown in Japanese Patent No. 59-43456 and including a single low frequency resonating chamber is effectively a hybrid muffler comprising both tubular and stamp formed components. The muffler shown in Japanese Patent No. 59-43456 would necessarily be substantially more complex with more tubular components if plural low frequency resonating chambers were provided.
U.S. Pat. No. 4,415,059 which issued to Hayashi on Nov. 15, 1983, shows an elongated stamp formed muffler comprising two generally cylindrical members linked in end-to-end relationship to effectively define a sausage-like structure. The muffler comprises a pair of internal plates which are stamp formed to define a single linear exhaust passage. A pair of external shells are stamp formed to surround the internal plates. The external shells are necked down at a generally central location to surround the stamp formed central linear tube and to thereby form chambers around portions of the tube. The tube passing through one of the chambers is perforated. Thus, the chamber surrounding the perforated portion of the single linear tube is an expansion chamber which attenuates a high frequency noise. The portion of the central tube in the other chamber is punch formed to define a pair of short straight flanged openings which extend perpendicular to the longitudinal axis of the central linear tube. The flanged openings are intended to function as tuning passages which communicate with a low frequency resonating chamber defined by the external shell.
The combination of short punch formed tuning passages and low frequency resonating chambers as shown in U.S. Pat. No. 4,415,059 is necessarily limited both functionally and structurally. In particular, the frequency of the sound to be attenuated by a combined tuning tube and low frequency resonating chamber is inversely proportional to the square root of the length of the tuning tube, inversely proportional to the square root of the volume of the low frequency resonating chamber and directly proportional to the square root of the cross sectional area of the tuning tube. Thus, longer tuning tubes can attenuate lower frequency sounds. Similarly, the larger the volume of the low frequency resonating chamber, the lower the frequency of the sound to be attenuated. Conversely, within certain limits, narrower tuning tubes attenuate a narrower range of low frequency sounds.
The punch formed tuning passage shown in U.S. Pat. No. 4,415,059 positively prevents the provision of long tuning tubes. Short tuning tubes or passages correspond to high frequency sound attenuation. Thus, the muffler shown in U.S. Pat. No. 4,415,059 would have limited effectiveness in attenuating the low frequency sounds for which tuning tubes are primarily intended. Any attempt to lengthen the punch formed passages shown in the muffler of U.S. Pat. No. 4,415,059 by widening the punch formed passages would be self-defeating since the radius squared is in the numerator of the equation which dictates the frequency of the sound to be attenuated. Thus, lengthening the punch formed passages of the muffler shown in U.S. Pat. No. 4,415,059 would in many instances have the effect of increasing the frequency of the sound attenuated. Furthermore, the punch formed construction of the tuning passage shown in U.S. Pat. No. 4,415,059 positively can not be curved. Thus, the length of these straight punch formed tuning passages extending orthogonal to the longitudinal through tube would be limited by the proximity of the outer shells.
Recently, several improvements to stamp formed mufflers have been made. In particular, U.S. Pat. No. 4,700,806 issued to Jon Harwood on Oct. 20, 1987, and U.S. Pat. No. 4,736,817 issued to Jon Harwood on Apr. 12, 1988, and both are assigned to the assignee of the subject invention. U.S. Pat. No. 4,700,806 and U.S. Pat. No. 4,736,817 are directed to extremely efficient, effective and inexpensive mufflers formed from stamp formed components. These mufflers include arrays of stamp formed tubes, which may include tuning tubes, and further comprise a plurality of chambers, which may include expansion chambers and low frequency resonating chambers. The mufflers shown in U.S. Pat. No. 4,700,806 and in U.S. Pat. No. 4,736,817 attenuate noise at least as well as, or better than, the prior art wrapped outer shell mufflers. However, these stamp formed mufflers can be manufactured from many fewer components and in processes that are well suited to automation. Additionally, the stamp formed mufflers are lighter than conventional mufflers.
Additional improvements to stamp formed mufflers have been made even more recently and are described and claimed in co-pending patent applications that are assigned to the assignee of the subject application. For example, U.S. patent application Ser. No. 061,876 is directed to an "EXHAUST MUFFLER WITH ANGULARLY ALIGNED INLETS AND OUTLETS". U.S. patent application Ser. No. 061,913 is directed to the "TUBE AND CHAMBER CONSTRUCTION FOR AN EXHAUST MUFFLER". U.S. patent application Ser. No. 106,244 described an efficient construction for a "STAMP FORMED MUFFLER WITH MULTIPLE LOW FREQUENCY RESONATING CHAMBERS" and enables at least two stamp formed tuning tubes and at least two low frequency resonating chambers to be provided in the muffler with a substantially reduced deformation of the stamp formed outer shell.
U.S. patent application Ser. No. 146,032 is directed to a "STAMP FORMED MUFFLER WITH CONFORMAL OUTER SHELL" to enable the muffler to conform to the limited available space on a vehicle. The disclosures of the above identified patents and applications assigned to AP Industries, Inc. are incorporated herein by reference.
Certain of the stamp formed mufflers described and illustrated in the preceding patents and patent applications assigned to AP Industries, Inc. have included an array of tubes defined by the stamp forming of internal plates and a plurality of chambers defined by the stamp forming of external shells. Certain of these chambers have been separated from one another by a stamp formed crease extending substantially entirely across the muffler. The crease has divided, for example, a low frequency resonating chamber from an expansion chamber of the muffler. Typically, the crease has included a plurality of outwardly convex arcuate portions disposed and dimensioned to engage the stamp formed tubes defined by the internal plates. Thus, these arcuate portions enable the stamp formed tubes to extend between the several chambers of the muffler. Typically, one such arcuate portion would engage a stamp formed tube extending to or from an inlet or outlet of a muffler, while at least one, and generally two, additional arcuate portions would engage tuning tubes of the muffler. Although the mufflers described in the related patents and applications identified above perform extremely well, it has been noted that the plural outwardly convex arcuate portions disposed in the crease between adjacent chambers effectively define depressions or reservoirs therebetween. Depending upon the location and orientation of the muffler on the vehicle and depending upon the environment in which the vehicle is employed, it has been noted that these depressions or reservoirs conceivably could retain liquids on the upper side of the muffler. In some environments, these liquids may contain salts or other potentially caustic chemicals. Although the metallic materials used for the stamp forming can generally resist the corrosive action of any retained liquids or salts, it is considered desirable to minimize any potential risk of premature failure of the muffler. Additionally, an overriding objective of most stamp forming processes is to minimize the amount of metal deformation required.
In view of the above, it is an object of the subject invention to provide a stamp formed muffler that does not include externally disposed reservoirs in which liquids, salts or other corrosive materials could be retained.
It is another object of the subject invention to provide a stamp formed muffler having at least one expansion chamber and a plurality of low frequency resonating chambers, but with only one tubular portion extending therebetween.
A further object of the subject invention is to provide a stamp formed muffler having tubular portions defined by internal plates and chambers defined by external shells and having only one tubular portion extending between adjacent chambers formed in the external shells.
An additional object of the subject invention is to provide a stamp formed muffler employing branch tuning with elongated tuning tubes.
Still a further object of the subject invention is to provide a stamp formed muffler having at least one tuning tube aligned at an acute angle to the inlet tube of the muffler.